John Krafcik, CEO of Waymo, said Friday that he’s stepping down from the top job at the self-driving car arm of Google parent company Alphabet.

Krafcik will be replaced by two executives who’ll lead as co-CEOs: Chief Operating Officer Tekedra Mawakana and Chief Technology Officer Dmitri Dolgov. Krafcik will remain an advisor to the company.

“After five and a half exhilarating years leading this team, I’ve decided to depart from my CEO role with Waymo and kick-off new adventures,” Krafcik wrote in an email to employees. “To start, I’m looking forward to a refresh period, reconnecting with old friends and family, and discovering new parts of the world.”

Waymo, started in 2009 as a Google project called Chauffeur, is a pioneer in autonomous cars, but the technology is still a long way from becoming mainstream. Last year, Krafcik announced that Waymo’s fleet of driverless vehicles had driven more than 20 million miles on public roads. Four years ago, the company began a pilot ride-hailing program picking up passengers in the Phoenix area. In 2019, Waymo began testing rides with Phoenix passengers in cars that were completely autonomous — without a safety driver behind the wheel.

Dolgov and Mawakana on Friday said they’re focused on developing the company’s technology, which is called the Waymo Driver. “We’re committed to working alongside you to build, deploy, and commercialize the Waymo Driver and drive the success of our incredible team and this company,” they said in a joint email to employees.